It's widely accepted by scientists now that it is inevitable that there are aliens living elsewhere in the universe.
The thing is that there is no likelihood that they could reach us, or we them.
The problem is distance...
Life can be based either on carbon atoms (as on Earth) or silicon. This is because of the valencies of the atoms which allow tremendous flexibility in bonding with other elements to form complex molecules capable of developing into RNA and DNA.
So for life to be possible, a planet must have a G2 sun or similar, must be of the right size at the right distance and orbit from the sun, and must be composed of the right minerals and have water and an atmosphere with oxygen and nitrogen.
There are billions of planets thoughout the universe which fulfill these criteria.
"Proxima Centauri b" is the nearest such planet, just 4.2 light years away.
The problem is - for humans to be able to travel at the speed of light is, as far as physicists know, logically and physically impossible.
Further, any species intelligent enough to invent such travel would probably cause its own extinction through technological excesses before it could achieve light-speed travel.
There is a lesson in this. Earth is our ideal home. There is no available Planet B. So we had better take good care of this one.